The study found non-Christians feel less self-assurance and fewer positive feelings if a Christmas tree was in the room.
Scientists who carried out the research claim the presence of a tree makes religious minorities feel 'excluded'.
Researchers at Simon Fraser University, in Canada, conducted the study using 77 Christians and 57 athiests and people of other faiths, including Buddhists and Sikhs.
The participants did not know the survey was about Christmas, and were asked to fill in questions about themselves both when a 12 inch Christmas tree was in the room and when it wasn't.
Non-celebrators reported fewer positive feelings and less self-assurance in the Christmas room. Christians were mostly cheered by the tree.
Christians, however, did report feeling more guilt when a tree was in the room, which, claim the researchers, suggests the holidays can be stressful.
Social psychologist Michael Schmitt decided to carry out the study after controversy over whether Christmas should be celebrated in public in case it offends non-Christians.
He said: "Simply having this 12-inch Christmas tree in the room with them made them feel less included in the university as a whole, which to me is a pretty powerful effect from one 12-inch Christmas tree in one psychology lab.
"I don't think it's really going to undermine anyone's experience of Christmas to tone it down.
"We're not suggesting 'no Christmas' or 'no Christmas displays at all,' but in contexts where we really do value respecting and including diversity in terms of religion, the safest option is not to have these kinds of displays.
"I understand why it might feel threatening to people.
"But I think if people do care about making a whole range of different kinds of people feel included and respected, then we can make some small changes that would go a long way toward creating a more multicultural or inclusive society."
The researchers reported their results in the Journal of Experimental Social Psychology.
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